This invention relates to a method for the quenching of the spent bed resulting from the reaction of organic halides with silicon metal to form organohalosilanes. It is well known in the art that the sPent bed resulting from the reaction of organic halides with silicon metal is highly susceptible to atmospheric oxidation, and in an unquenched state can represent a serious potential fire hazard.
It is postulated that such fires result from the autoxidation of silicon hydride (SiH) and polysilane (SiSi) moities present in the spent bed. These oxidative processes may be represented by the following chemical reactions: EQU 2 SiSi+O.sub.2 .fwdarw.2 SiOSi EQU 2 SiH+O.sub.2 .fwdarw.2 SiOH
It is known that the oxidizable SiSi and the SiH moities may be destroyed by reaction with water, catalyzed by either strong acids or bases. Eaborn, C., Organosilicon Compounds, Butterworths Scientific Publications, London, 1960, p. 200 and p. 354. These reactions are: EQU SiSi+2 H.sub.2 O .fwdarw.2 SiOH+H.sub.2 EQU SiH+H.sub.2 O.fwdarw.SiOH+H.sub.2
However, neither autoxidant is readily attacked by water, nor by bases as weak as sodium bicarbonate (pH 8.4). These reactions proceed with great difficulty because of the tendency to form a siloxane-rich hydrophobic shell around the spent bed particles hindering the reaction. The siloxanes are formed as the result of residual chlorosilanes in the spent bed: EQU SiCl+H.sub.2 O.fwdarw.SiOH+HCl EQU 2 SiOH.fwdarw.SiOSi+H.sub.2 O
In addition to this siloxane-rich hydrophobic shell, the inventors have found, that in the case of spent beds from the reaction of organic halides with silicon, an inert carbon containing shell is also formed around the spend bed silicon particles. These two types of shells are believed by the inventors to be the principle hindrance to effective quenching of spent beds resulting from the reaction of organic halides with silicon.
Breneman, et al., U.S. Pat. No. 4,690,810, issued Sept. 1, 1987, discloses the use of lime to convert a liquid chlorosilane mixture contaminated with various metal chlorides and minor amounts of metals into environmentally acceptable products. No mention is made of quenching a spent bed resulting from the reaction of silicon metal with an organic halide.
Hosokawa, U.S. Pat. No. 4,724,122, issued Feb. 9, 1988, discloses a method for treating the reaction residue from the preparation of organochlorosilanes or chlorosilanes by the reaction of silicon metal with a chlorinated hydrocarbon. The disclosed method consisted of combining the reaction residue with water and granulating the residue. The granulated residue (spent bed) was then coated with an inert organic powder.